3D Gravity Modelling Research Articles

Chern–Simons-like formulation of exotic massive 3D gravity models

We investigate the Chern–Simons-like formulation of exotic general massive gravity models within the framework of third-way to three-dimensional gravity. We classify our construction into two main approaches: one using torsional cosmological Einstein and exotic massive gravity equations, and the other a torsion-free approach. The former approach, while mathematically appealing, precludes the construction of critical exotic models where the central charges vanish. In contrast, the latter approach has a wider parameter space and allows for the construction of critical models. An explicit example of an exotic general model is provided to illustrate both methods. Our methodology represents the first step towards establishing the most general Chern–Simons-like formulation of third-way to three-dimensional gravity, which would enable the study of identifying its bulk/boundary unitary sector.

Benefits of integrating seismic and gravity data in a subsalt environment: A case study at block BM-C-33, deepwater Campos Basin, offshore Brazil

Imaging subsalt layers is challenging in the BM-C-33 block in the Campos Basin’s ultradeep waters. This block is important because it has three significant gas and condensate discoveries in the presalt carbonate and volcanic reservoirs—Seat, Gávea, and Pão de Açucar. Understanding basement morphology is essential to better define the petroleum system in the area. To that end, we performed a 2D gravity modeling exercise along a northwest–southeast section using seismic interpretation as input to reduce the ambiguity of the modeling exercise. To achieve this, we fixed the main sedimentary horizons and their densities (calculated via well-log information) to better estimate the top of the basement morphology. This interpretation strategy better delineated the presalt sedimentary section and the complex structural framework with two asymmetric grabens bounded by a prominent horst, interpreted as a migration focusing high in the BM-C-33 area. In addition, our findings show that obtaining clear images remains challenging even after extensive processing of the seismic data set. We suggest that seismic node acquisition with ultralong offsets and multiazimuthal illumination and then carefully processing the data is required to accurately reveal the area’s prerift section and basement morphology under study.

Crustal structure and tectonic evolution of the Pranhita-Godavari Rift: A comprehensive study using edge enhancement techniques and 2D gravity modeling

The Pranhita-Godavari Rift basin is a significant tectonic feature in peninsular India. The Bouguer gravity anomaly digital grids from the gravity map of India (after NGRI-GSI, 2006) were analyzed to present a detailed discussion of the Pranhita-Godavari rift basin’s crustal structure and contribute to understanding its regional geology (i.e., Sediment thickness, depth of the basement, Conrad, and Moho) and tectonics. Using advanced techniques like the horizontal gradient method (HGM), first vertical derivative (FVD), and tilt derivative (TDR), we successfully mapped the regional tectonic features. The identified key lineaments and faults have trends primarily in NW-SE, WNW-ESE, NNE-SSW to N-S, and NE-SW directions.The depth of the Moho, Conrad, and basement was computed using 2D gravity modeling. The modeling reveals significant findings, including substantial crustal thickening within the rift, with Moho depths ranging from 38.6 km to 41 km, indicating considerable tectonic subsidence and sediment accumulation. Conrad discontinuity depths vary between 18 km and 26 km, reflecting complex crustal deformation associated with rifting processes. Basement depths range from 3.5 km to 6.2 km; the Alluvium, Barakar, Sullavai, and Pakhal sediments are deposited over the Archean basement, highlighting differential subsidence within the rift compared to adjacent cratonic regions. Additionally, several major and newly observed faults were mapped using 3D Euler deconvolution and 2D gravity modeling. The Ahiri-Tippapuram, Godavari Valley, Kinnerasani Godavari, Koddam, and Kolleru Lake faults were identified, extending to the Moho with significant downthrows, indicating varied tectonic activity. These findings provide valuable insights into the tectonic evolution and structural dynamics of the PGR, offering a deeper understanding of rift-related processes and aiding future research in the region.

Integration of 2D and 3D electrical resistivity tomography and 2D gravity modeling to evaluate groundwater investigations in the Burka Uke catchment area, western Ethiopia

The increasing demand for water resources due to the expanding infrastructure and growing population of Uke town, West Ethiopia, necessitates a comprehensive understanding of groundwater potential within the Burka Uke catchment. The aims and objectives of this study are to identify a map of the aquifer by characterizing the subsurface earth, basement rock depth, resistivity and density of geological layers, their thicknesses, and structural features. The investigation integrates electrical resistivity tomography and gravity modeling to delineate potential groundwater zones and their structural controls. Electrical resistivity tomography profiles (1, 4, and 6) revealed low resistivity zones indicative of potential aquifers. The significant resistivity contrast (378 to 1412 Ω.m) suggests a high fracture density, potentially enhancing groundwater storage. The Bouguer gravity anomaly map, separated into regional and residual components, displayed values ranging from 51.79 to 41.59 mGal, highlighting density variations in the subsurface. As a result, analysis of the residual gravity anomaly map identifies north–south striking fault elements, indicating their influence on groundwater flow.The combined 2D and 3D ERT data also revealed a 2D gravity model of the aquifer from which the concentration extended throughout the study area. Data validation with previously drilled wells has confirmed the effectiveness of the geophysical methods used in identifying potential groundwater zones. This study provided critical information for the sustainable management of existing groundwater and demonstrated the effectiveness of integrating geophysical techniques to delineate and characterize aquifers in water-stressed areas.

Efficient large-scale 3D gravity modeling using a fast evaluate kernel matrix combined with compressed matrix techniques

A fast calculated kernel matrix method is coupled with a compressed matrix technique to solve the large-scale gravity forward-modeling problem. This method accelerates the coefficient matrix computation by reducing the arctangent, logarithm, and multiplication functions in the prismatic gravity analytical expression. In addition, the use of the compressed matrix technique presents a significant advantage in that it does not require the storage of redundant kernel matrices, further reducing the memory requirements and computation time. Moreover, the discrete convolution of the compressed matrix with density is executed through the 2D fast Fourier transform (FFT). Two typical synthetic models are used to test the performance of the novel algorithm. The results demonstrate that the developed algorithm is approximately 15 times faster than the traditional algorithm. Concurrently, it demands almost 1/7th of the memory while ensuring equivalent computational accuracy. To further illustrate the capability of the algorithm, we apply our method to the terrain correction of an airborne gravity data set using a real digital elevation model. Our approach efficiently calculates 250,000 observation points across 25 million cells in only 5.42 s, compared with 234.81 s for the latest 2D Gauss-FFT method.

3D Gravity and magnetic inversion modelling for geothermal assessment and temperature modelling in the central eastern desert and Red Sea, Egypt

The Central Eastern Desert and Red Sea region have emerged as a significant area of interest for geothermal energy exploration, owing to their unique geological characteristics and active tectonic activity. This research aims to enhance our understanding of the region's geothermal potential through a comprehensive analysis of gravity and magnetic data. By utilizing a 3D gravity inversion model, a detailed examination of subsurface structures and density variations was conducted. Similarly, a 3D magnetic inversion model was employed to investigate subsurface magnetic properties. Integration result from the Pygimli library ensured robustness and accuracy in the inversion results. Furthermore, a temperature model was developed using the WINTERC-G model and inversion techniques, shedding light on the thermal structure and potential anomalies in the study area. The analysis of the Bouguer gravity map, 3D gravity inversion model, and magnetic data inversion yielded significant findings. The Red Sea exhibited higher gravity values compared to the onshore Eastern Desert, attributed to the presence of a thinner and denser oceanic crust as opposed to the less dense continental crust in the Eastern Desert. The 3D gravity inversion model revealed distinct variations in density, particularly high-density zones near the surface of the Red Sea, indicating underlying geological structures and processes. Conversely, density gradually decreased with depth along the onshore line, potentially influenced by a higher concentration of crustal fractures. The magnetic data inversion technique provided additional insights, highlighting areas with demagnetized materials, indicative of elevated temperatures. These findings were consistent with the correlation between high-density areas and low magnetic susceptibility values, reinforcing the proposition of increased heat transfer from the Red Sea. Comparative analysis of temperature profiles further confirmed the presence of elevated temperatures in promising zones, emphasizing the geothermal potential associated with heat transfer from the Red Sea.This research contributes to the understanding of the geothermal resources in the Central Eastern Desert and Red Sea region. The results from gravity and magnetic data inversions, combined with temperature profiles, provide valuable information for future geothermal exploration and utilization efforts. The findings underscore the importance of geothermal energy in achieving sustainability and contribute to the global discourse on renewable energy sources.

Deformation under a Young Volcanic Covered Area in Southern Garut, Indonesia: Insight from 3D Gravity Modelling

Destructive earthquakes are frequently related to inland active faults. In recent years, a significant number of shallow earthquakes with low magnitude have occurred in southern Garut, West Java, Indonesia. Two earthquakes, with magnitudes of M4.2 and M3.9 in 2016 and 2017, respectively, have caused significant damage and were interpreted as indications of an active fault. We used publicly available gravity data to infer the subsurface structure that may be related to recent seismic activity. We used spectral analysis and filtering techniques for the regional-residual anomaly separation and anomaly enhancement to show the basin structure in the study area. 3D gravity inversion modelling was performed to obtain the subsurface density distribution. The result indicates the sedimentary layers with a density of 2.4 to 2.5 gr/cm3 with an underlying basement with a density of 2.65 gr/cm3. An intra-basin basement high with an NE-SW trend divides the basin into two sub-basins. This local basement high can be associated with a magmatic intrusion body and a series of young volcanic bodies located at the northeastern end of the basin. Our results emphasize a possible strong interaction between the tectonic and magmatic activities in this region.

Gravity Field Numerical Analysis and Depth Structure of the South-Eastren Caucasus

In this paper, the gravity anomalies of the Bouguer of the Absheron, Shamakhi-Gobustan and Pricaspian-Guba oil- and gas-bearing regions are interpreted by the 3D prism method. According to this model, a part of the earth's crust covering the crystalline basement is considered as a set of many prisms located nearby. The depth of the surface of the crystalline basement is calculated taking into account the change in density at the bottom of the low velocity zones of the upper part of the earth's crust and the dependence of the density difference on depth according to a quadratic law.
 For interpretation of the gravity anomalies in the Absheron, Shamakhy-Gobustan and Pricaspian-Guba regions, a sedimentary basin viewed as, a number of prisms placed in juxtaposition. The decrease of density contrast in sedimentary basins approximated by, a quadratic function. The contour map is sampled at 1160 equispaced points with 5 km interval. The depths to the interface separating sedimentary were calculated using a generalized computer program GR3DSTR for 3-D inversion of gravity data either for a constant density contrast or for a variable density contrast with depth.
 From 3D gravity model of the sedimentary layer, it was found that the maximum depth is in the areas of Gyuzdek and Meraza (11 km), and the minimum is in the areas of Gonakkend, Gilazi, Garabulag, Dubrar (4 km).
 The depth of the sedimentary layer around the Agzibirchala well varies within 6 km. The correlation of the distribution of the thickness of the sedimentary layer on the site with the seismic section and well sections was determined.
 KEYWORDS – gravity anomaly, sedimentary basin, oil and gas fields.

Influence of thick lithomargic soil cover on Bouguer gravity low: Imprints from passive continental margin of southwestern India

The Periyar Plateau in central Kerala is characterized by a strong negative Bouguer gravity field around three major islands of a strongly negative field of the value of -150 mGal. Detailed gravity studies reveal that these islands of strong negative field are of a shallow nature and are not traceable in the 1/4° average gravity grids. Spectral analysis of Bouguer anomaly map and 2D gravity modelling of Periyar Plateau region reveal the average depth of the shallow source layer is as shallow as 700-1000 m, which is correlatable with the layer of lateritic/lithomargic soil cover and the underlying weathered country rock having a density of 2.2 g/cc. Such a strong influence on the regional gravity field is due to the wide contrast in the densities of the lateritic cover and the primary rocks of the basement. These results underline the need to recognize the strong influence of such alteration zones on the regional gravity fields, especially the tropics, a factor not always considered.

Architectural rift geometry of the Rio do Peixe Basin (Brazil): Implications for its tectonic evolution and Precambrian heritage

Preexisting shear zones in the basement may influence the formation of normal faults in rift environments. However, the specific role and interaction between these preexisting shear zones and younger rift faults in controlling the growth of normal faults remain an area of limited understanding. The Rio do Peixe Basin (RPB), located in Brazil, was the subject of a comprehensive study using integrated airborne magnetic analysis, 2D and 3D seismic interpretation, and 3D gravity modeling. This study investigated tectonic evolution and Precambrian heritage by examining the role of basement structures in controlling the internal geometry of the RPB. The integration of geophysical data supported by field data showed that the underlying basement structures significantly influence the geometry of the basin sedimentary fill. E–W-striking structures controlled the opening of the RPB and the development of the depocenters of the basin. NE–SW-striking structures influenced the segmentation of the depocenters and, consequently, the internal geometry of the basin. Furthermore, the study revealed the migration of depocenters toward the NE associated with developing the NE–SW-striking segment of the Portalegre Fault attributed to the basin-opening process. By investigating the underlying crustal architecture, this comprehensive geophysical study sheds light on the architectural rift geometry of the RPB. The findings underscore the influence of basement structures on the internal basin architecture and provide valuable insights into its tectonic evolution and Precambrian heritage.

Overdeepenings in the Swiss plateau: U-shaped geometries underlain by inner gorges

We investigated the mechanisms leading to the formation of tunnel valleys in the Swiss foreland near Bern. We proceeded through producing 3D maps of the bedrock topography based on drillhole information and a new gravimetric survey combined with modelling. In this context, the combination of information about the densities of the sedimentary fill and of the bedrock, together with published borehole data and the results of gravity surveys along 11 profiles across the valleys, served as input for the application of our 3D gravity modelling software referred to as PRISMA. This ultimately allowed us to model the gravity effect of the Quaternary fill of the overdeepenings and to produce cross-sectional geometries of these troughs. The results show that 2–3 km upstream of the city of Bern, the overdeepenings are approximately 3 km wide. They are characterized by steep to oversteepened lateral flanks and a wide flat base, which we consider as a U-shaped cross-sectional geometry. There, the maximum residual gravity anomaly ranges between − 3 to − 4 mGal for the Aare valley, which is the main overdeepening of the region. Modelling shows that this corresponds to a depression, which reaches a depth of c. 300 m a.s.l. Farther downstream approaching Bern, the erosional trough narrows by c. 1 km, and the base gets shallower by c. 100 m as revealed by drillings. This is supported by the results of our gravity surveys, which disclose a lower maximum gravity effect of c. − 0.8 to − 1.3 mGal. Interestingly, in the Bern city area, these shallow troughs with maximum gravity anomalies ranging from − 1.4 to − 1.8 mGal are underlain by one or multiple inner gorges, which are at least 100 m deep (based on drilling information) and only a few tens of meters wide (disclosed by gravity modelling). At the downstream end of the Bern area, we observe that the trough widens from 2 km at the northern border of Bern to c. 4 km approximately 2 km farther downstream, while the bottom still reaches c. 300 to 200 m a.s.l. Our gravity survey implies that this change is associated with an increase in the maximum residual anomaly, reaching values of − 2.5 mGal. Interestingly, the overdeepening’s cross-sectional geometry in this area has steeply dipping flanks converging to a narrow base, which we consider as V-shaped. We attribute this shape to erosion by water either underneath or at the snout of a glacier, forming a gorge. This narrow bedrock depression was subsequently widened by glacial carving. In this context, strong glacial erosion upstream of the Bern area appears to have overprinted these traces. In contrast, beneath the city of Bern and farther downstream these V-shaped features have been preserved. Available chronological data suggest that the formation of this gorge occurred prior to MIS 8 and possibly during the aftermath of one of the largest glaciations when large fluxes of meltwater resulted in the fluvial carving into the bedrock.

Crustal and tectonic structure of Northern Mozambique inferred by 2D gravity modeling

The northern region of Mozambique has a complex geological history, with an evolution that spans from the Precambrian Era to the Phanerozoic Era. In this work, we have integrated gravity and geothermal data to delineate the geotectonic evolution of the region, by estimating the thickness of the crust and the lithosphere through which was essential to generate a representative crustal model. It was necessary to complement the knowledge of structural geometry and tectonic evolution of the region. The data used in this study are the Bouguer and geoid anomalies, topography data, and radiogenic heat. These data were pre-processed, topography and geoid anomaly data were filtered by low-pass filter in the frequency and harmonic domains to remove undesirable effects associated with the sources. The data were used to estimate the thickness of the crust and lithosphere, as well as to determine the mean density distribution within the mantle. This was achieved by using a one-dimensional approach, considering the principle of local isostatic compensation, associated with equations governing the distribution of temperature in the crust. The Bouguer anomaly was used to generate a representative crustal 2D model of this region. The results showed that the crust is thinner in Nampula and Cabo Delgado provinces, with thickness ranging from 27 to 31 km, whereas in Niassa varies between 33 and 39 km. The analysis of lithospheric thickness indicates that the provinces of Nampula and Cabo Delgado present a thinning of the lithosphere, with values ranging from 150 to 165 km. Rather than Niassa province which exhibits a thicker lithosphere, ranging from 165 to 195 km. The obtained results underwent a comparative analysis with prior investigations, unveiling a noteworthy concurrence among these findings.

Coarse graining pure states in AdS/CFT

We construct new Euclidean wormhole solutions in AdSd+1 and discuss their role in UV-complete theories, without ensemble averaging. The geometries are interpreted as overlaps of GHZ-like entangled states, which arise naturally from coarse graining the density matrix of a pure state in the dual CFT. In several examples, including thin-shell collapsing black holes and pure black holes with an end-of-the-world brane behind the horizon, the coarse-graining map is found explicitly in CFT terms, and used to define a coarse-grained entropy that is equal to one quarter the area of a time-symmetric apparent horizon. Wormholes are used to derive the coarse-graining map and to study statistical properties of the quantum state. This reproduces aspects of the West Coast model of 2D gravity and the large-c ensemble of 3D gravity, including a Page curve, in a higher-dimensional context with generic matter fields.

Identification of Mount Sirung Geothermal Potential based on Land Surface Temperature and 3D Gravity Model

According to the Ministry of Energy and Mineral Resources 2021 data, first ranks in the list of 10 provinces with the lowest electrification ratio in Indonesia. One of the geothermal prospect areas in East Nusa Tenggara is Mount Sirung. This research was conducted in August 2022 which aims to identify geothermal systems. Gravity data was obtained from the GGMPlus 2013 with a total of 3819 data. Land Surface Temperature (LST) is used as supporting data with a surface temperature approximately 26.1 – 29.5°C because there are manifestations of hot springs at Mount Sirung. Based on the derivative analysis, there are four trajectories in the northwest-southeast direction with reverse faults and normal faults as the geothermal control system of Mount Sirung. The results of 3D gravitational inversion modeling are estimated that there is clay interspersed with breccia with a density of 2.34 – 2.39 g/cm3 as clay cap at 0 – 600 m, and lava interspersed with sandy tuff as a reservoir with a density of 1.98 – 2.03 g/cm3 at 700 – 1400 m. Based on these results and discussions, Mount Sirung is proven to have geothermal potential which can be utilized as a source of electrification in East Nusa Tenggara.

Crustal structure and isostatic compensation beneath the South China Sea using satellite gravity data and its implications for the rifting and magmatic activities

Opening of the South China Sea (SCS) was triggered by the breakup of south-eastern Eurasia and the southward drifting of the Palawan-Reed Bank microcontinent, as various prior studies have suggested. The young, moderately magmatic, rifted northern margin of the SCS is vital for investigating the relationship among magmatism, rheology, and structural evolution. This paper integrates satellite gravity anomaly, elevation/bathymetry, geoid, and seismic velocities to investigate continental breakup, magmatism, and rifting beneath the South China Sea. Source depths of 146, 31.5, and 8 km derived from the spectrum of Bouguer gravity anomalies suggest the average depths of the lithospheric base, continental, and oceanic crustal bases, respectively. Correspondingly, gravity Moho ranges from 8 km beneath the rifting center of SCS to 42 km in the Indo-China block. It is worth mentioning that the isostatic Moho from the Airy and flexural models were highly correlated with gravity Moho with correlation coefficients of ∼1. From the ratio between geoid and topography and our estimate of the vertical tectonic stress, the seamounts and reefs (Shuangfeng Basin: SB, Reed Bank: RB, Macclesfield Bank: MB) have a deep compensation depth. In contrast, the other parts (Manila Trench: MT, Phu Khan Basin: PK, East Sub Basin: ESB) have a smaller depth of compensation. 2D gravity modelling suggests the crustal thinning of the oceanic basin, and the thickening of the continental boundary implies the opening of the SCS, which is connected and happened at the same time as the northern subduction of the proto-SCS. The Gravity modelling also suggests a large rifting event within the lithosphere that favors mantle upwelling.

3D inversion modelling of gravity data for identification of subsurface structures in the mud volcano area of Sedati, Sidoarjo

Many mud volcanoes are found in Central Java and East Java in the north, but research on mud volcanoes is still limited. This research focuses on the Sedati mud volcano area, Sidoarjo with a research area of 500x400 meters. Measurement of gravity method data with 88 points spaced 50 meters to determine the value of rock density and subsurface structure of Sedati mud volcano area. From the data that has been obtained, data processing is carried out to obtain a map of the distribution of regional and residual gravity anomaly values. From the anomaly data, 3D inversion was carried out to obtain a map of the subsurface structure. The 3D gravity inversion modelling results show that there is high density rock block which is interpreted as a basin that holds the reservoir from the mud volcano. Near the surface and around the mudflow in the study area, the distribution of low density is caused by the presence of mud content. There is a possibility that there is a fault zone with a west-east direction from the study area. The results of the 3D gravity model incision show that the weak zone in the study area is a zone of accumulation of mud which has a density value of 1.8 g/cm3 at a depth of 20 meters to 500 meters.

Pole-skipping points in 2D gravity and SYK model

We represent the first investigation of pole-skipping on both the gravity and field theory sides. In contrast to the higher dimensional models, there is no momentum degree of freedom in (1 + 1)−dimensional bulk theory. Thus, we then consider a scalar field mass as our degree of freedom for the pole-skipping phenomenon instead of momentum. The pole-skipping frequencies of the scalar field in 2D gravity are the same as higher dimensional cases: ω = −i2πTn for positive integers n. At each of these frequencies, there is a corresponding pole-skipping mass, so the pole-skipping points exist in (ω, m) space. We also compute the pole-skipping points of the SYK model in (ω, h) space where h is the dimension of the bilinear primary operator. We find that there is a one-to-one correspondence of the pole-skipping points between the JT gravity and the SYK model. To obtain the pole-skipping points, we need to consider the parameter ϵ related to the chemical potential on the horizon of charged JT gravity and the particle-hole asymmetric parameter mathcal{E} of the complex SYK model as shift parameters. This highlights the ϵ − mathcal{E} correspondence in relation to pole-skipping phenomenon.

3D Seismic reflection evidence for lower crustal intrusions beneath the Faroe–Shetland Basin, NE Atlantic Margin

Lower crustal intrusion is considered to be a common process along volcanic or magma-rich passive margins, including the NE Atlantic Margin, where it is thought to have occurred during phases of Paleogene magmatism, both prior to and during continental break-up between NW Europe and Greenland. Evidence of Paleogene magmatism is prevalent throughout the sub-basins of the Faroe–Shetland Basin as extensive lava flows and pervasive suites of igneous intrusions. However, in contrast with other areas located along the NE Atlantic Margin, no lower crustal reflectivity indicative of lower crustal intrusion has been documented beneath the Faroe–Shetland Basin. The nearest documentation of lower crustal reflectivity and interpretation of lower crustal intrusion to the Faroe–Shetland Basin is NW of the Fugloy Ridge, beneath the Norwegian Basin of the Faroese sector. Despite this, the addition of magma within the lower crust and/or at the Mohorovičić discontinuity is thought to have played a part in Paleogene uplift and the subsequent deposition of Paleocene–Eocene sequences. Advances in sub-basalt seismic acquisition and processing have made significant improvements in facilitating the imaging of deep crustal structures along the NE Atlantic Margin. This study used broadband 3D seismic reflection data to map a series of deep ( c. 14–20 km depth) high-amplitude reflections that may represent igneous intrusions within the lower crust beneath the central-northern Corona Ridge. We estimate that the cumulative thicknesses of the reflections may be >5 km in places, which is consistent with published values of magmatic underplating within the region based on geochemical and petrological data. We also estimate that the total volume of lower crustal high-amplitude reflections within the 3D dataset may be >2000 km 3 . 2D gravity modelling of a seismic line located along the central-northern Corona Ridge supports the interpretation of lower crustal intrusions beneath this area. This study provides evidence of a potential mechanism for Paleogene uplift within the region. If uplift occurred as a result of lower crustal intrusions emplaced within the crust during the Paleogene, then we estimate that c. 300 m of uplift may have been generated within the Corona Ridge area.

Fast 3D gravity and magnetic modelling using midpoint quadrature and 2D FFT

To avoid the problem of the traditional methods consuming large computational resources to calculate the kernel matrix and 2D discrete convolution, we present a novel approach for 3D gravity and magnetic modelling. This method combines the midpoint quadrature method with a 2D fast Fourier transform (FFT) to calculate the gravity and magnetic anomalies with arbitrary density or magnetic susceptibility distribution. In this scheme, we apply the midpoint quadrature method to calculate the volume element of the integral. Then, the convolution of the weight coefficient matrix with density or magnetization is efficiently computed via the 2D FFT. Finally, the accuracy and efficiency of the proposed algorithm are validated by using an artificial model and a real topography model. The numerical results demonstrate that the proposed algorithm’s computation time and the memory requirement are decreased by approximately two orders of magnitude compared with the space-wavenumber domain method.

Carbonate-rock aquifers in arid environments (central Tunisia, Western Mediterranean province): gravity and time domain electromagnetic methods investigations

Gravity and time domain electromagnetic (TDEM) methods were used in this study to investigate the subsurface hydrogeology of the carbonate-rock aquifer in arid environments (central Tunisia, Western Mediterranean province). The El Houdh basin can be considered an appropriate case for evaluating the vulnerability of groundwater resources under present-day climate change. The identification of structural context and the discontinuities affecting the Eocene or Campanian to Maastrichtian carbonates is an important key to recognize water recharge and discharge pathways and to develop effective and long-term groundwater exploration strategies. First, we have produced an available residual gravity field using a specific Gaussian filter. Then, we generated derivative maps, Euler deconvolution solutions map and a 3D gravity model to delineate different anomalies and to estimate the depth-to-basement parameter and the subsurface density contrasts. Positive and negative anomalies mapping and 3D gravity modelling showed that the El Houdh basin is associated with an asymmetric ‘perched syncline’ with a segmentation into NE–SW sub-basins (local negative residual anomalies) separated by NW–SE lineaments. The TDEM survey was calibrated using boreholes to image the karst saturated and unsaturated zone and to deduce the epikarst and endokarst relationship. Finally, the proposed method provides a fast and valuable approach for better management of hydrogeological exploitation. Thematic collection: This article is part of the Climate change and resilience in Engineering Geology and Hydrogeology collection available at: https://www.lyellcollection.org/cc/climate-change-and-resilience-in-engineering-geology-and-hydrogeology